CN115380226A

CN115380226A - Apparatus and method for detecting photons and charged particles and uses thereof

Info

Publication number: CN115380226A
Application number: CN202080076738.XA
Authority: CN
Inventors: G·D·略萨·利拉塞尔; C·拉卡斯塔·利拉塞尔; J·巴里奥·托阿拉
Original assignee: Consejo Superior de Investigaciones Cientificas CSIC; Universitat de Valencia
Current assignee: Consejo Superior de Investigaciones Cientificas CSIC; Universitat de Valencia
Priority date: 2019-11-07
Filing date: 2020-11-04
Publication date: 2022-11-22
Also published as: ES2823949B2; WO2021089899A1; EP4057034A4; ES2823949A1; US20220373698A1; EP4057034A1; US11796689B2

Abstract

The present invention relates to a solution for determining events related to photons and charged particles, which is useful in therapy using methods related to hadron therapy. In one aspect of the invention it relates to an arrangement of a sandwich-type structure with a photon detection panel (1) and a charged particle detection panel (2), which can be suitably associated with respective sensors. Methods of detecting photons and charged particles using the above-described apparatus are also included. Finally, the specific use of the object of the invention in hadron therapy is described.

Description

Apparatus and method for detecting photons and charged particles and uses thereof

Technical Field

The object of the present invention is in the field of physical technology, more specifically in the field of particle detection.

Background

One of the major drawbacks of hadron therapy is that there is no effective way to determine in real time whether the radiation dose is being applied correctly to the intended site. Detecting secondary particles that escape from the tissue when irradiated provides a method for monitoring the treatment. Currently, positron emission tomography is the only method used, but has serious drawbacks in terms of detection efficiency and performance, and therefore alternative monitoring methods are being studied.

One of these alternatives includes detecting gamma radiation emitted by the tissue. There are different types of detectors currently under development for detecting emitted gamma radiation, but they have not been put into use. Both collimated and compton cameras have been developed.

Collimating the camera is a simple method, close to clinical use, but inefficient, and provides only a one-dimensional view of the dose application variation.

Compton cameras are used for or research in different fields of radiation detection and localization: astrophysics, national security, positioning of radioactive sources after nuclear disasters, medical imaging, and recent hadron therapy monitoring. In each case they contain detectors that have to be optimized for a specific scene. This type of camera provides a more efficient monitoring method. However, their response is also limited because in a clinical application environment, a large number of events are detected due to noise, which degrades the signal, which events are considered to be the interaction of charged particles or radiation photons with the detector or detection panel.

In Traini, giacomo et al, physica Medical, european Journal of Medical Physics, vol.34, pages 18-27, an apparatus for detecting the source of secondary charged particles generated after interaction of a carbon ion beam with patient tissue is described and relates the emission curve of these particles to the position of the Bragg peak and hence to the radiation dose. The apparatus forms part of a large apparatus comprising a PET (positron emission tomography) detector. The charged particle detector consists of a series of planes made of scintillator fibers coupled to sipms (silicon photomultipliers) followed by two scintillators.

Document US2014110592 describes a compton camera for image reconstruction that detects particles (gamma radiation and electrons) produced in compton interactions, also describes different modules with different arrangements, and analyzes the results to determine the compton cone.

The document WO 2016140371 A1 describes an apparatus capable of detecting the trajectory (tracking) of the energy of the electron deposit emitted by compton interaction to better determine the incident direction of the gamma ray. The invention described herein aims to solve the problem of uncertainty of the first interaction point of a gamma ray when multiple scattering occurs at the detector or when another gamma ray interacts simultaneously, while the electron detector is the same as in the case of the first compton interaction of a photon.

However, tracking requires the use of accurate (often expensive) detectors capable of detecting various electronic interactions, whereas detectors that determine trajectory typically have low photon detection efficiency.

In document US 9535016 A1, the claimed system comprises means for improving the efficiency of CT (computed tomography) images by using discrete events in the patient. Electron detectors that detect electron escapes to exclude such events are proposed in this document.

In the system described in the aforementioned document, the object to be imaged is located between the source and the gamma radiation detection panel. The photons of the present invention must be low energy photons, on the order of photons used in CT, as they are intended to interact with and scatter in objects.

In most cases, the electrons emitted in the compton interaction do not escape from the detection panel in view of the low energy of the photons in this document. If they escape, their energy is low and it is unlikely that they will reach the object or the second detector. A problem that arises in this document is that it is proposed to add electronic detectors for this purpose, which take up a part of the energy that is not deposited in the detector and therefore distort the measurement of the event. Thanks to the electronic detector, these events can be rejected. The electron detector claims to reject such an event, but the electrons do not interact with the object nor with the second detector.

None of the solutions existing in the prior art is able to determine which recorded events are good and which are not so, in order to discard the latter and improve the signal-to-noise ratio (SNR) without having to reconstruct traces. They are also difficult to be compatible with structural imaging and reconstruction methods, which will allow better determination of the irradiated area and the tumor in therapeutic applications.

In general, compton detectors, particularly those that use high energy photons to acquire an image, detect a large number of background events that distort the acquired image. These events are generated both by incident particles on the first detector, which are different from the photons from the object, and by secondary particles generated when the photons interact with the first detector or with the continuous detector.

These particles interact in different detectors, producing random coincidences that the system registers randomly as good events, thus producing a noisy background in the image. The number of particles, and thus the number of background events, increases with increasing photon energy.

The proposed invention aims at detecting background events generated by particles generated in the detector, as well as any kind of additional charged particles (electrons, positrons, protons, ions, charged debris) from the incident radiation in order to remove them from the image, which none of the state-of-the-art compton cameras achieve. In addition, it provides information about the event to improve the resolution of the device.

Summary of The Invention

The object of the present invention is to improve the signal-to-noise ratio of photon detection devices by detecting incident charged particles or particles resulting from photon interactions and to be useful for monitoring the radiation dose in hadron therapy.

The detection arrangement of the first aspect of the invention comprises several detection planes, interspersed charged particle detectors and photon detectors, preferably from gamma radiation.

Thus, the detection device of the first aspect of the present invention can distinguish between photons and charged particles, and reduce the background noise problem caused by charged particles, thereby improving the SNR.

Preferably, in a first embodiment, the detection means consists of several detection planes combining a central charged particle detector (e.g. silicon detector, scintillator fiber) between two photon detectors and interacting photons in the photon detection panel, and two detectors optimized for detecting (compton interaction) high-energy photons, called first photon detector and second photon detector (between hundreds of keV and 10-20 MeV). The charged particle detector makes it possible to determine whether the signal detected in the second photon detector corresponds to photons scattered in the first photon detector or to a charged particle.

In an alternative embodiment, the apparatus further comprises a front charged particle detector, preferably located between the incident radiation source and the first photon detecting panel, and the central charged particle detector is positioned behind the first photon detecting panel, on the opposite side to the front charged particle detecting panel. Behind the central charged particle detection panel a second photon detection panel is placed.

The central charged particle detection panel is capable of detecting charged particles resulting from photon interactions in the first photon detection panel, generating a signal, providing the option of rejecting and considering this information to reconstruct events, helping to more accurately determine the energy deposited in the first photon detector and whether an event is valid or invalid.

The front charged particle detection panel is capable of detecting charged particles in incident radiation and distinguishing them from photons.

The present invention aims to obtain an image of the photon emission distribution (activated by radiotracer, by external radiation or by radioactivity), for example the body of a patient, so that it is the object or patient acting as the source, in front of a photon detection panel or a positively charged particle detection panel, depending on the embodiment.

In the present invention, the photons are not intended to interact with the object, but rather with the first photon detector. The invention is useful in situations where there are charged particles striking the device or photons of sufficient energy to generate secondary particles and may cause increased noise in the image.

Unlike other detectors with similar applications, the apparatus of an alternative embodiment of the present invention comprises two charged particle detection panels and two photon detection panels in a sandwich-type structure, capable of distinguishing between different types of particles, determining whether an incident particle is a photon (an active event) or a charged particle (an active or inactive event). It is also possible to determine whether the photons continue their trajectory after interacting in each detector, or whether the particles produced by the photons in their interaction with the detector have all their energy stored in the detector or escaped.

This detection capability makes it possible to reconstruct each event and determine which of the recorded events are good and which are not, in order to discard the latter and to improve the signal-to-noise ratio (SNR), thereby improving the performance of the apparatus of the invention compared to existing or developing systems.

Furthermore, the device is compatible with structural imaging and reconstruction methods, such as tomography (CAT) and Magnetic Resonance Imaging (MRI), allowing better determination of the irradiated area and the tumor.

Thus, a second aspect of the invention is a method of detecting photons and charged particles.

Also, in a third aspect of the invention, the invention aims at enabling monitoring of the use of the administration of a radiation dose in hadron therapy, preferably based on gamma radiation photons emitted by the tissue when irradiated.

Drawings

To supplement the description which is being made and to help better understand the characteristics of the invention according to a preferred practical exemplary embodiment thereof, a set of drawings is attached as an integral part of said description, in which the following is described in an illustrative and non-limiting way:

fig. 1A and 1B show schematic views of a first embodiment of the device object of the invention.

Fig. 2 shows a schematic view of a second embodiment of the device object of the invention.

Fig. 3 shows a schematic representation of a third embodiment of the device object of the invention.

Fig. 4 shows a schematic view of a fourth embodiment of the device object of the invention.

Fig. 5 shows a schematic view of a fifth embodiment of the device object of the invention.

Fig. 6 shows a schematic view of a sixth embodiment of the device object of the invention.

Fig. 7 shows two graphs showing the recorded coincidence values as a function of the thickness of each Si detector of the charged particle detector for incident 3MeV (left) and 6MeV (right) photons.

Fig. 8 shows two graphs showing the percentage of noise events for incident 3MeV (left) and 6MeV (right) photons that can be detected by a charged particle detector.

Fig. 9 shows two graphs showing the percentage of primary photons (from the beam) interacting in silicon for 3MeV and 6MeV, respectively, on the left and right.

Fig. 10 illustrates an embodiment of noise reduction in a 2D image simulating bragg peaks.

Detailed Description

In a first preferred embodiment of the device corresponding to the first aspect of the invention, as shown in fig. 1A, there is a device for detecting photons and charged particles having a sandwich-type structure, onto which a radiation source impinges, wherein there is first a first photon detection panel (11) which causes compton scattering of incident photons such that their wavelength increases, losing part of the energy before passing towards a subsequent panel.

Behind the first photon detection panel (11), on the side opposite to the radiation source, a central charged particle detection panel (22) is positioned for detecting charged particles resulting from photon interactions in the first photon detection panel (11), generating signals, providing the option of rejecting and considering this information to reconstruct events, helping to determine more accurately the energy deposited in the first photon detection panel (11) and whether an event is valid or invalid. This improves the result of the device.

Finally, in this first embodiment, the apparatus comprises a second photon detection panel (12) located behind the central charged particle detection panel (22), on the opposite side from the incident radiation source, wherein photons scattered in the first photon detection panel interact. The central charged particle detection panel (22) may also distinguish whether a particle impinging on the second photon detection panel (12) is a photon or a charged particle.

Furthermore, in a second embodiment, as shown in fig. 1B, the device may comprise a front charged particle detection panel (21), preferably made of a material comprising silicon, and located between the incident radiation source and the first photon detection panel (11), the front charged particle detection panel detecting charged particles from the incident radiation and from the environment, the signal being generated when charged particles pass said front detection panel (21).

In a possible third embodiment of the invention, such as the one shown repeatedly in fig. 2, the apparatus comprises, in addition to the two scintillator crystals (in this case made of LaBr3, but it can be made of LaBr3, ceBr3 or CdTe or CZT semiconductor detectors) and the front charged particle detector (21) and the central charged particle detector (22) consisting of silicon detectors, a rear charged particle detection panel (23) which detects the charged particles of the incident radiation passing through the second photon detection panel (12), generating a signal.

In an exemplary embodiment performed by simulation, a 3/6MeV photon or electron beam is made to impinge on and record events that produce signals in two photon detection panels (11, 12) that coincide in time, and it is investigated whether a silicon charged particle detector (21,22) can fulfill its function of helping to distinguish charged particles from photons, i.e., to distinguish valid events from background noise.

In a fourth embodiment of the invention, shown in fig. 3, the apparatus further comprises a second central charged particle detection panel (22).

In a fifth embodiment of the invention, the apparatus further comprises a third photon detection panel (13). Between the three photon detection panels (11, 12, 13), a central charged particle detection panel (22) and a rear charged particle detection panel (23) may be disposed between the second and third photon detection panels (22, 23). Furthermore, a front charged particle detection panel (21) may be located between the radiation source and the first photon detection panel (11), and/or a rear charged particle detection panel (26) may be located behind the third photon detection panel (13).

Alternatively, in this fifth embodiment, as shown in fig. 4, between the radiation source and the first photon detection panel (11), two front charged particle detection panels (21) and two central charged particle detection panels (22) may be located between the first photon detector (11) and the second photon detection panel (12). After the latter, two rear charged particle detection panels (23) are placed.

In a sixth alternative embodiment of the invention shown in fig. 5, the apparatus comprises, in addition to the elements of the first embodiment described in fig. 1B, two pairs of transverse charged particle detectors (24). Each of the transverse charged particle detectors (24) of each pair is positioned on either side of, perpendicular to, the first photon detector (11) or the second photon detector (12). In this way they are able to detect charged particles of incident radiation that pass through the photon detection panels (11, 12) and deviate from their vertical trajectory.

In a seventh embodiment of the invention, shown in fig. 6, which includes all the elements of the first embodiment shown in fig. 1B, the apparatus additionally comprises two pairs of aligned charged particle detectors (25), the detectors of each pair being located next to each other, and each of the pairs of aligned charged particle detectors (25) being located after the first photon detector (11) and the second photon detector (12). In this way, these detectors are able to detect charged particles passing through photon detection panels (11, 12) that deviate from their vertical trajectory.

Furthermore, in all embodiments described above, the apparatus may comprise a first signal detector associated with each photon detector (11, 12, 13) and a second signal detector associated with each charged particle detection panel (21, 22, 23, 24, 25, 26).

Two possibilities are provided herein to achieve the objectives of the method of the second aspect of the invention: in the first case, charged particles reach the device, and in the second case, gamma radiation strikes the scintillator crystals of the first photon detection panel (11) and secondary particles are generated causing the event to be ineffective.

To simulate the first case, a gamma ray beam or a 3MeV electron beam is impinged on the device of fig. 3, which comprises four charged particle detection panels (21, 22, 23), between which each photon detection panel (11, 12) is arranged on the surface of the front charged particle detection panel (21), on the left side of fig. 3.

In this case, the photon detectors (11, 12) are made of LaBr3, with dimensions of 32X 35mm2, a thickness of 10mm, and a spacing of 30mm from one another. Events that produce signals in the two photon detectors (11, 12) that coincide in time are recorded and it is investigated whether the charged particle detectors (21, 22, 23) fulfill their function of helping to distinguish valid events from background noise.

Upon analysis of the results, 0.715% of the events were observed to interact in both photon detection panels (11, 12) simultaneously, and were therefore recorded by the device as potentially valid events. However, these events will correspond to noise, since the interaction is not due to photons. Wherein almost all events (0.714%) generate signals in the front charged particle detection panel (21) which is located at the incident side of the radiation of the charged particle detection panel (11), in front of the first photon detection panel (11), so that they are easily rejected.

In order to illustrate the efficiency of the device in different cases, in the second case, various simulations were performed, with a 3MeV or 6MeV photon beam impinging on the device and varying the thickness of the photon detectors (11, 12) between 50 and 1000 microns.

The percentage of events detected in the three cases was studied:

in the first case mentioned in the graph of fig. 7, the total simulated events (100 ten thousand per thickness of charged particle detection panel (21, 22, 23)) depend on the thickness of the charged particle detection panel (21, 22, 23) for the incident 3MeV and 6MeV photons, corresponding to the left and right graphs, respectively. The recorded values are applicable to two photon detection panels (11, 12) consistent with the size and geometry under study, including good events and bad or noisy events.

In the second case mentioned in the graph of fig. 8, for incident 3MeV and 6MeV radiation photons, in the left and right graphs, respectively, the percentage of noise events that the front charged particle detection panel (21) is able to detect in the events recorded as coincident in each case. These noise events may reduce the response of the first photon detector (21), but due to the front charged particle detection panel (21), they may be detected and removed from the analysis.

In the third case mentioned in the graph of fig. 9, the percentage of primary photons (from the incident radiation beam) interacting in the front charged particle detection panel (21) in the event recorded as coincidence in each case (3 MeV and 6MeV for the left and right side, respectively). These events are unwanted noise events generated by including the front charged particle detection panel (21) in the device.

It is an object of the invention to be able to detect a significant percentage of noise events (almost all incident charged particles and 20-30% recorded coincidence) that would degrade its response through the front charged particle detection panel (21) and can be removed. Noise events generated by the introduction of the front charged particle detection panel (21), which in turn reduces the performance of the device, are kept at a low level. Thus, performance is improved compared to an apparatus including only a photon detection panel.

Fig. 10 shows the noise reduction effect in an image simulating bragg peaks. In the image on the left, all events are included. In the right image, events that interacted with Silicon have been removed. As can be seen from fig. 10, noise in the image is significantly reduced due to the use of the present invention.

The image in fig. 10 is obtained using an apparatus based on an embodiment similar to that in fig. 3, where there is a first photon detecting panel (11) between two charged particle detecting panels (21, 22) and a second photon detecting panel (12) between two other charged particle detecting panels (22, 23).

Claims

1. An apparatus for detecting photons and charged particles, the apparatus comprising:

a first photon detection panel (11) which causes compton scattering of incident radiation and charged particles such that its wavelength increases, losing part of its energy, producing a signal,

-a central charged particle detection panel (22) behind the first photon detection panel (11), on the side opposite to the incident radiation, identifying charged particles generated in the first photon detection panel (11), generating a signal, and

-a second photon detection panel (12) behind the central charged particle detection panel (22), on the opposite side to the first photon detection panel (11), wherein scattered photons and/or charged particles generated in the first photon detection panel (11) interact, generating a signal.

2. The device for detecting photons and charged particles of claim 1, further comprising a front charged particle detection panel (21) located between the incident radiation and the first photon detection panel (11), which identifies charged particles from the incident radiation or environment, generating a signal.

3. The arrangement for detecting photons and charged particles according to claim 2, further comprising a rear charged particle detector (23) detecting charged particles resulting from photon interactions in the second photon detecting panel (12).

4. A device for detecting photons and charged particles as defined in claim 3, further comprising a second central charged particle detection panel (22).

5. The arrangement for detecting photons and charged particles of claim 1, further comprising a third photon detection panel (13) located behind the second photon detection panel (12), and a rear charged particle detection panel (23) positioned between the second photon detection panel (12) and the third photon detection panel (13).

6. The device for detecting photons and charged particles of claim 5, further comprising a front particle detection panel (21) located between the radiation source and the first photon detection panel (11).

7. The arrangement for detecting photons and charged particles of claim 5, further comprising a rear charged particle detection panel (26) located behind the third photon detection panel (13).

8. The arrangement for detecting photons and charged particles according to claim 5, further comprising a front particle detection panel (21) located between the radiation source and the first photon detection panel (11), and a rear charged particle detection panel (26) located behind the third photon detection panel (13).

9. The arrangement for detecting photons and charged particles of claim 4, further comprising a second front charged particle detection panel (21), a second rear charged particle detection panel (23), a third photon detection panel (13) behind the rear particle detection panel (23), and two rear charged particle detection panels (26) behind the third photon detection panel (13).

10. The device for detecting photons and charged particles of claim 2, further comprising a plurality of pairs of transverse charged particle detectors (24), a first pair being positioned perpendicular to each side of said first photon detector (11) and a second pair being positioned perpendicular to each side of said second photon detector (12).

11. The arrangement for detecting photons and charged particles as defined in claim 2, further comprising pairs of aligned charged particle detectors (25), the aligned charged particle detectors (15) of each pair being positioned in alignment adjacent to each other, one of said pairs being located between the first photon detector (11) and the central charged particle detector (22), the second pair being located after the second photon detector (12).

12. The arrangement for detecting photons and charged particles according to any of the preceding claims, further comprising a first signal detector associated with each photon detector (11, 12, 13) and a second signal detector associated with each charged particle detection panel (21, 22, 23, 24, 25, 26).

13. The arrangement for detecting photons and charged particles according to any of the previous claims, wherein the photon detection panel (11, 12, 13) is a detector based on a scintillator material selected from LaBr3, ceBr3, GAGG or a semiconductor detector selected from CdTe and CZT.

14. Method for detecting photons and charged particles with the device according to any of the preceding claims, characterized in that it comprises the following steps:

determining a signal level in at least one of the charged particle detection panels (21, 22, 23, 24, 25, 26) by a signal detector, and

a negative event is defined when the signal level determined in the previous step is not 0.

15. Use of a device according to any one of claims 1 to 13 for monitoring radiation dose in hadron therapy.

16. Use of the apparatus according to any one of claims 1 to 13 for image reconstruction.